Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
  • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0011—Sample conditioning
  • G01N33/0016—Sample conditioning by regulating a physical variable, e.g. pressure or temperature

Definitions

• the invention relates to a method for gas detection using a gas-selective membrane whose permeability for a specific gas is temperature-dependent.
• the membrane temperature For gas detection with such gas-selective membranes, it is known to adjust the membrane temperature to a temperature value at which the membrane's gas permeability for the gas type to be detected is maximum.
• the membrane is typically heated when the gas permeability is maximum at a temperature greater than room temperature.
• the gas measurement signal is superimposed by an offset signal that depends, for example, on the temperature or the age of the gas sensor.
• the gas upstream of the sensor can be removed by evacuation using pumps to measure the offset signal in a vacuum without gas.
• DE102016200270 It is known to perform offset-reduced gas detection using two membranes, one of which is exposed to the measuring gas and the other is not.
• the invention is based on the object of creating a method for gas detection with a gas-selective membrane in which the influence of the offset signal on the measurement signal is reduced.
• the gas detection according to the invention is carried out using a gas-selective membrane with temperature-dependent permeability for the gas to be detected.
• a temperature device is designed to change the temperature of the membrane.
• the temperature device is preferably a heater.
• a cooling device is also conceivable if the permeability of the membrane at a temperature that is lower than the Ambient temperature of the membrane is maximum.
• a detector is provided and configured to detect a measurement signal depending on the amount of gas passing through the membrane.
• the detector can be a gas measuring device, such as a mass spectrometer, or a pressure measuring device, such as a total pressure measuring device.
• the permeability of the gas-selective membrane for the gas to be detected should be greater at one of the two membrane temperatures than at the other.
• the permeability may be greater at the first membrane temperature than at the second.
• the permeability is maximum at the first temperature.
• the difference between the various membrane temperature values set and changed using the temperature device should be between approximately 2 K and 10 K, and preferably between approximately 3 K and 6 K. This applies in particular to the difference between the first temperature value and the second temperature value.
• the temperature device is preferably designed as a heater, with at least the first membrane temperature value being greater than the temperature of the area surrounding the membrane. Before a subsequent, new membrane temperature value is set, the heater can be switched off for a few seconds, with the set first temperature value and the set second membrane temperature value each being above the membrane's ambient temperature.
• the measured values of the measurement signal are advantageously recorded in each affected interval only after a few seconds, preferably after approximately 2 to 5 seconds, after a new temperature value has been set on the temperature device or the parameter influencing the membrane temperature has been changed.
• the gas detection device 10 is shown schematically with a gas-selective membrane 12 with temperature-dependent permeability.
• the membrane 12 is heated by a temperature device 14 in the form of a heater with heating elements arranged on the membrane 12.
• the heater is controlled via a control device 16.
• the control device 16 is part of the temperature device 14. Parameters are entered via the control device 16 that influence the power of the heater and thus the heating effect on the membrane 12. As a result, a parameter can be changed via the control device 16 that influences the heater 14 and changes the temperature of the membrane 12.
• the heater 14 is attached to the membrane 12 in such a way that gas flows from the direction of the arrow 18 in Fig. 1 through the heater 14 and through the membrane 12. With respect to the flow direction according to the arrow 18 in Fig.
• a detector 20 in the form of a pressure measuring device is arranged downstream, ie, behind the membrane 12. Gas permeating through the membrane 12 enters the detector and increases the measured pressure there.
• the detector 20 can also be a gas detector, e.g., in the form of a mass spectrometer.
• the detector 20 is connected to an evaluation unit 22, which receives and evaluates the measurement signal from the detector 20. With the aid of the evaluation device 22, the measured values of the measurement signal generated by the detector 20 are recorded and the inventive subtraction of the measured values is carried out.
• Fig. 2 the measurement signal S of the detector 20 is plotted against time t in seconds.
• the heater 14 is activated via the control device 16 and a first parameter P 1 is specified, which causes the heater 14 to heat the membrane 12 to a first membrane temperature T 1 that is greater than the room temperature in the environment of the gas detection device 10.
• the temperature T 1 can be 80 °C.
• the temperature T 1 is the temperature at which the membrane 12 has a comparatively high permeability for the gas to be detected, in the present embodiment, helium.
• the measuring signal S increases, for example in the form of an electrical measuring current, as in Fig. 2 shown, to a maximum value, which is measured at a time t of approximately 10 seconds as the first measured value H n .
• the parameter of the heating device 14 is changed from P 1 to P 2 via the control device 16, which results in the membrane temperature falling from the value T 1 to the value T 2.
• the second membrane temperature T 2 is lower than the first membrane temperature T 1 and is nevertheless above the room temperature in the vicinity of the Gas detection device 10.
• the second membrane temperature T 2 is a temperature at which the permeability of the membrane 12 for the gas to be detected is lower than at T 1 .
• the measurement signal S drops from its local maximum due to the temperature T 1 to a local minimum due to the temperature T 2 and is measured at a time t of approximately 20 seconds as the second measured value L n .
• the parameter P 2 is changed back to P 1 via the control device 16, thus starting another cycle of periodic repetition of the temperature change.
• the resulting first interval is Fig. 2 referred to as n and extends from 0 to a time t of 20 seconds.
• the subsequent interval n+1 of the periodic repetition of the temperature switching begins. Changing the parameter of the control device 16 from P 2 to P 1 results in an increase in the membrane temperature towards the first membrane temperature T 1 .
• a linear drift of the offset of the measurement signal can be eliminated as follows:
• the first measured values H n , H n+1 , H n+2 etc. and the second measured values L n , L n+1 etc. of the respective intervals n, n+1, n+2 etc. are recorded by the evaluation device 22.
• the evaluation device 22 forms a difference between the first measured value and the second measured value, wherein in the present embodiment the mean value is formed from the first measured values H n , H n+1 of subsequent intervals n, n+1 as (H n + H n+1 )/2 and from this mean value the second measured value recorded between the two first measured values H n , H n+1
• the mean values of both the first and the second measured value can be calculated, whereby the mean values can also be calculated over two or more intervals.
• the second measured value L n , L n+1 is recorded in each interval at a time when the membrane temperature has been set to the second temperature T 2 , thus minimizing the permeability of the membrane 12.
• the second measured value L n , L n+1 approximately corresponds to the offset signal that does not result from gas passing through the membrane 12.
• the evaluation unit 22 makes an assessment as to whether the measurement signal S results from a gas to be detected and in what quantity this gas is present, based on the difference signal ⁇ S n , because the influence of the offset signal on the difference signal is reduced.
• the membrane temperature is controlled by the control device 16 and the heater 14 by first measuring the membrane temperature using a measuring device not shown in the figures. Depending on the temperature measurement result, the control device 16 causes the membrane 12 to heat up using the heater 14 until the higher, desired temperature value is reached.
• the difference between the two temperature levels T 1 , T 2 is only 5 K in the present embodiment.
• the signal swing ⁇ S between the two temperature levels can be obtained from the averaging of two adjacent high temperature signals, H n + H n+1 , and the intermediate signal of the lower temperature level L n .
• the drift is in Fig. 2 recognizable as a negative slope of the dashed lines of the signal amplitudes decreasing from left to right.
• the method according to the invention is preferably used for indoor air monitoring.
• the sensor does not necessarily have to react quickly. Active air supply is also not absolutely necessary.
• the membrane temperature T 1 , T 2 is varied in order to change the permeability of the membrane 12 and thus the sensor sensitivity of the gas detection device 10.
• This change in sensitivity is accompanied by a change in the measurement signal S, in this case a current change, which is proportional to the partial pressure of the gas to be detected (helium).
• the variation in the membrane temperature is achieved by changing the parameter P 1 , P 2 .
• the parameters are set to the lowest possible values in order to generate the smallest possible continuous sensor current (measurement signal S) at atmospheric pressure in order not to unnecessarily reduce the service life of the sensor.
• the change in the parameter P 1 , P 2 takes place in the present embodiment according to Fig. 2 every 10 seconds, switching back and forth between parameters P 1 and P 2. After changing the parameter, a delay of approximately 8 seconds is observed before the respective measured value H n , L n is measured, in order to allow the time required for heating control to elapse.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
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• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Examining Or Testing Airtightness (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

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• 2020
  • 2020-06-24 DE DE102020116660.5A patent/DE102020116660A1/de active Pending
• 2021
  • 2021-05-25 US US18/009,584 patent/US20230204552A1/en active Pending
  • 2021-05-25 EP EP21729459.4A patent/EP4172618B1/de active Active
  • 2021-05-25 CN CN202180044106.XA patent/CN115769072B/zh active Active
  • 2021-05-25 JP JP2022580240A patent/JP7642685B2/ja active Active
  • 2021-05-25 WO PCT/EP2021/063924 patent/WO2021259581A1/de not_active Ceased
  • 2021-05-25 KR KR1020227044834A patent/KR20230027064A/ko active Pending

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